Backup Plan When Zoom Phone System Is Down

We noticed that zoom system was down last week and we were unable to call at that stage. Does zoom provide a plan that can separate the desk phone and VoIP app? You can choose to use VoIP as default. But when there's a problem, network isn't working for example. You then choose to use only desk phone which goes through traditional landline. And vice versa, if the landline is down, you can choose to go only VoIP. This is an open discussion as network problem or power outage happens very often.